Surface-coating binders

Abstract

Surface-coating binders based on a reaction product of Mannich bases, obtained from polyhydric phenols, secondary amines and formaldehyde, with epoxy resins. The Mannich bases and/or the epoxy resins carry hydroxyl groups, bonded to aliphatic structures, which have been converted to urethane groups by reaction with partially blocked polyisocyanates. When protonized and diluted with water, the surface-coating binders may be used as cationic electrocoatings.

We claim: 
     
       1. A surface-coating binder which is substantially free from epoxide groups and water-dilutable by protonization with acids, said binder being a reaction product of (A) from 25 to 90 percent by weight of a Mannich base obtained from (a 1 ) a polyhydric phenol which contains two or more aromatic rings and is free from ether groups, and which can be partially replaced by   (a 2 ) a monohydric or polyhydric phenol which contains two or more aromatic rings and contains an ether group,   (b 1 ) a secondary amine which contains one or two hydroxy alkyl groups, mixed with   (b 2 ) a secondary dialkylamine or dialkoxyalkylamine and   (c) formaldehyde or a formaldehyde donor, the amount of (c) is at least one mole per mole of (b 1  +b 2 ), and     (B) from 75 to 10 percent by weight of an epoxy resin, wherein (a 1 ) is a phenol of the general formula ##STR6##  where X is a straight-chain or branched, divalent aliphatic radical of 1 to 3 carbon atoms or is SO 2 , SO, O or CH 2  --NR--CH 2  (where R is alkyl of 1 to 6 carbon atoms) and   (a 2 ) is at least one further condensed phenol, which contains at least one phenolic hydroxyl group and in addition one or more ether groups in the molecule, having the general formula   HO--B--[O--E--O].sub.n --H     or     HO--B--[O--E--O].sub.n --P        where B is ##STR7##  and X has the above meanings, E is a radical, containing hydroxyl groups, obtained by addition of an epoxy compound to a phenolic hydroxyl group, P is phenyl or alkylphenyl, and n is an integer from 1 to 3,   (b 1 ) is a dialkanolamine of alcohols of 2 to 6 carbon atoms,   (b 2 ) is a secondary dialkylamine having the general formula ##STR8##  where R 1  and R 2  are identical or different and are a straight-chain or branched aliphatic radical of 2 to 10 carbon atoms, which may or may not contain alkoxy groups,   the weight ratio of components (b 1 ) and (b 2 ) being from 1:10 to 1:0.1,   at least a part of the hydroxyl groups bounded to aliphatic structures of the Mannich base (A) or of the epoxy resin (B) have been converted to urethane groups by reaction with a partially blocked polyisocyanate.     
     
     
       2. A surface-coating binder as set forth in claim 1, wherein the Mannich base is obtained from a phenol of the formula ##STR9## where the hydroxyl groups are in the ortho position or para position to X and where X is a straight-chain or branched chain divalent aliphatic radical of 1 to 3 carbon atoms or is SO 2 , SO, O or CH 2  --NR--CH 2  (where R is alkyl of 1 to 6 carbon atoms) as component (a 1 ). 
     
     
       3. A surface-coating binder as set forth in claim 1, wherein the Mannich base is obtained from bisphenol A as component (a 1 ). 
     
     
       4. A surface-coating binder as set forth in claim 1, wherein the component (a 2 ) is obtained from a reaction product of a diglycidyl ether of bisphenol A or a dihydric to tetrahydric aliphatic alcohol with bisphenol A and optionally with phenol. 
     
     
       5. A surface-coating binder as set forth in claim 1, wherein the Mannich base is obtained from components (a 1 ) and (a 2 ) employed in a weight ratio of from 1:0.1 to 1:5. 
     
     
       6. A surface-coating binder as set forth in claim 1, wherein the Mannich base is obtained from diethanolamine as component (b 1 ). 
     
     
       7. A surface-coating binder as set forth in claim 1, wherein the Mannich base is obtained from di-n-butylamine as component (b 2 ). 
     
     
       8. A surface-coating binder as set forth in claim 1, wherein the Mannich base is obtained from the components (a 1  +a 2 ) and (b 1  +b 2 ) employed in a molar ratio (a 1  +a 2 ):(b 1  +b 2 ) of from 1:0.75 to 1:3, and an amount of component (c) of at least 1 mole per 1 mole of (b). 
     
     
       9. A surface-coating binder as set forth in claim 1, wherein a reaction product of a polyhydric phenol of the formula ##STR10## where X has the meaning given in claim 2, with epichlorohydrin, is used as component B). 
     
     
       10. A surface-coating binder as set forth in claim 23, wherein component (B) is a reaction product of bisphenol A or pentaerythritol with epichlorohydrin. 
     
     
       11. A surface-coating binder as set forth in claim 1, wherein the reaction of component (A) with component (B) is carried out under conditions where from 0.2 to 0.9 epoxide group of component (B) is present per phenolic hydroxyl group of component (A). 
     
     
       12. A surface-coating binder as set forth in claim 1, wherein the aliphatic hydroxyl groups of the epoxide resin (B) have been reacted with a partially blocked polyisocyanate, at such a ratio between the amounts used that from 0.01 to 1.0 mole of urethane groups are present per mole of basic nitrogen in the finished binder. 
     
     
       13. A surface-coating binder as set forth in claim 1, wherein an aromatic diisocyanate blocked with an aliphatic alcohol has been used as partially blocked polyisocyanate. 
     
     
       14. A surface-coating binder as set forth in claim 1, wherein the partially blocked polyisocyanate is a toluylene diisocyanate which is blocked with one mole of an aliphatic monoalcohol of 2 to 8 carbon atoms. 
     
     
       15. A surface coating binder as set forth in claim 1, wherein a reaction product of a dihydric to tetrahydric aliphatic alcohol with epichlorohydrin is used as component (B). 
     
     
       16. A surface coating binder as set forth in claim 1, wherein the aliphatic hydroxyl groups of component (a 2 ) of the Mannich base (A) have been reacted with a partially blocked polyisocyanate, at such ratio between the amounts used that from 0.01 to 1.0 mole of urethane groups are present per mole of basic nitrogen in the finished binder. 
     
     
       17. A process as set forth in claim 4, wherein the reaction products have molecular weights of from 650 to 1300 and where any excess of epoxide groups has been eliminated. 
     
     
       18. A surface-coating binder as set forth in claim 1, wherein the urethane groups are formed by reaction with from 3 to 15%, based on solids, of partially blocked polyisocyanate.